Visibility state retrieval (VSR) operations are used to decide whether one or more specified rows should be visible to a given query or not. In database systems whose transaction processing is based on multi-version concurrency control (MVCC) or snapshot isolation, a specified row's visibility to a given query is typically decided based on when the row was recently modified and when the query was started. Generally, the states of rows that need to be checked for a query are iterated one by one individually. However, for analytical queries which may need to access very large number of rows in a table or entire rows in a table, this row-oriented VSR operation incurs a high transactional cost because it is done one-by-one for each row.
In the drawings, like reference numbers generally indicate identical or similar elements. Additionally, generally, the left-most digit(s) of a reference number identifies the drawing in which the reference number first appears.